// Copyright (c) 2012 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef GPU_COMMAND_BUFFER_COMMON_COMMAND_BUFFER_H_
#define GPU_COMMAND_BUFFER_COMMON_COMMAND_BUFFER_H_

#include "gpu/command_buffer/common/buffer.h"
#include "gpu/command_buffer/common/constants.h"
#include "gpu/gpu_export.h"

namespace base {
class SharedMemory;
}

namespace gpu {

// Common interface for CommandBuffer implementations.
class GPU_EXPORT CommandBuffer {
public:
    struct State {
        State()
            : get_offset(0)
            , token(-1)
            , error(error::kNoError)
            , context_lost_reason(error::kUnknown)
            , generation(0)
        {
        }

        // The offset (in entries) from which the reader is reading.
        int32 get_offset;

        // The current token value. This is used by the writer to defer
        // changes to shared memory objects until the reader has reached a certain
        // point in the command buffer. The reader is responsible for updating the
        // token value, for example in response to an asynchronous set token command
        // embedded in the command buffer. The default token value is zero.
        int32 token;

        // Error status.
        error::Error error;

        // Lost context detail information.
        error::ContextLostReason context_lost_reason;

        // Generation index of this state. The generation index is incremented every
        // time a new state is retrieved from the command processor, so that
        // consistency can be kept even if IPC messages are processed out-of-order.
        uint32 generation;
    };

    struct ConsoleMessage {
        // An user supplied id.
        int32 id;
        // The message.
        std::string message;
    };

    CommandBuffer()
    {
    }

    virtual ~CommandBuffer()
    {
    }

    // Check if a value is between a start and end value, inclusive, allowing
    // for wrapping if start > end.
    static bool InRange(int32 start, int32 end, int32 value)
    {
        if (start <= end)
            return start <= value && value <= end;
        else
            return start <= value || value <= end;
    }

    // Initialize the command buffer with the given size.
    virtual bool Initialize() = 0;

    // Returns the last state without synchronizing with the service.
    virtual State GetLastState() = 0;

    // Returns the last token without synchronizing with the service. Note that
    // while you could just call GetLastState().token, GetLastState needs to be
    // fast as it is called for every command where GetLastToken is only called
    // by code that needs to know the last token so it can be slower but more up
    // to date than GetLastState.
    virtual int32 GetLastToken() = 0;

    // The writer calls this to update its put offset. This ensures the reader
    // sees the latest added commands, and will eventually process them. On the
    // service side, commands are processed up to the given put_offset before
    // subsequent Flushes on the same GpuChannel.
    virtual void Flush(int32 put_offset) = 0;

    // As Flush, ensures that on the service side, commands up to put_offset
    // are processed but before subsequent commands on the same GpuChannel but
    // flushing to the service may be deferred.
    virtual void OrderingBarrier(int32 put_offset) = 0;

    // The writer calls this to wait until the current token is within a
    // specific range, inclusive. Can return early if an error is generated.
    virtual void WaitForTokenInRange(int32 start, int32 end) = 0;

    // The writer calls this to wait until the current get offset is within a
    // specific range, inclusive. Can return early if an error is generated.
    virtual void WaitForGetOffsetInRange(int32 start, int32 end) = 0;

    // Sets the buffer commands are read from.
    // Also resets the get and put offsets to 0.
    virtual void SetGetBuffer(int32 transfer_buffer_id) = 0;

    // Create a transfer buffer of the given size. Returns its ID or -1 on
    // error.
    virtual scoped_refptr<gpu::Buffer> CreateTransferBuffer(size_t size,
        int32* id)
        = 0;

    // Destroy a transfer buffer. The ID must be positive.
    virtual void DestroyTransferBuffer(int32 id) = 0;

// The NaCl Win64 build only really needs the struct definitions above; having
// GetLastError declared would mean we'd have to also define it, and pull more
// of gpu in to the NaCl Win64 build.
#if !defined(NACL_WIN64)
    // TODO(apatrick): this is a temporary optimization while skia is calling
    // RendererGLContext::MakeCurrent prior to every GL call. It saves returning 6
    // ints redundantly when only the error is needed for the CommandBufferProxy
    // implementation.
    virtual error::Error GetLastError();
#endif

private:
    DISALLOW_COPY_AND_ASSIGN(CommandBuffer);
};

} // namespace gpu

#endif // GPU_COMMAND_BUFFER_COMMON_COMMAND_BUFFER_H_
